This invention concerns a coil-forming head as set forth in the main claim.
The coil-forming head according to the invention is applied in machines to form coils starting from continuous and substantially rectilinear semi-worked pieces arriving from the rolling mill or from another similar source, such as for example rods, round pieces or similar.
In the state of the art, coiling machines consist of a rotary coil-forming head comprising a tube, terminally shaped as a spiral, with an inlet axis coaxial to the rolling axis, substantially horizontal, and the outlet axis tangent to the nominal theoretical diameter of the coils which are to be obtained.
The rolled stock leaving the finishing stand is sent inside the shaped tube which bends to form at outlet a succession of coils with a defined pitch and diameter. The coils formed in this way fall and are deposited onto a roller-way to be cooled and sent to the collection and/or stacking zone.
The shaped tube is made to rotate around the rolling axis by suitable motor means at a velocity such that the outlet section, tangent to the nominal diameter of the coils to be obtained, has a peripheral velocity substantially equal to the rolling speed.
In this way, the kinetic energy possessed by the rolled stock entering the shaped tube can be completely discharged inside the said tube and the coils emerge substantially stationary with respect to an outside observer.
The kinetic energy possessed by the rolled stock is mainly balanced, inside the shaped tube, by the friction generated between the rolled stock and the inner walls of the tube due to the components of force normal to the direction of movement to which the rolled stock is subjected.
Apart from this, a part of the kinetic energy is balanced by a state of traction which is determined upstream of the coil-forming head; said traction is balanced since the trailing end of the rolled stock is held between the rollers of the finishing stand.
When the trailing end of the rod exits from the finishing stand, the balance of the traction forces continues to be ensured due to the presence of a drawing assembly located upstream of the coil-forming head, the function of which is substantially to brake and control the trailing end of the rolled stock.
But when the trailing end leaves the drawing assembly too, an unbalance is created in the forces, since the traction on the rolled stock generated by the coil-forming head is no longer balanced by an equal and contrary force acting upstream of the head.
This unbalance in the forces causes a violent acceleration of the trailing end which is translated into an increased velocity of the material compared with the peripheral velocity of the shaped tube.
If not controlled, this increased velocity would tend to cause the formation of one or more trailing-end coils with a much larger diameter than the desired nominal diameter.
To overcome this shortcoming, the state of the art provides, at the outlet of the shaped tube, a stationary cylindrical ring with a diameter slightly more than the nominal diameter of the coils, the function of which is to prevent the formation of trailing-end coils with a diameter much greater than the nominal diameter.
An example of this embodiment is shown in U.S. Pat. No. 3,563,488.
The trailing-end segment, therefore, which would tend to form coils of a greater diameter, stops against the ring, and vents the energy deriving from the impact by bending the round piece.
In this way, an omega shaped bend, or loop, is formed in the trailing-end segment of the rolled stock, located on the last coil.
The formation of this loop is extremely undesirable since it causes problems of blockages in the collection and stacking operations; it is therefore necessary to provide manually to at least partly straighten the loop in order to limit such problems to a minimum. Moreover, the loop must necessarily be eliminated manually before the finished reels are tied.
All this entails an undesirable increase in the work force, and also a waste of material.
Various solutions have been proposed to overcome this disadvantage which businessmen in this field have long been complaining about.
One solutionxe2x80x94to instantaneously conform the velocity of the coil-forming tube to that of the trailing end of the rolled stockxe2x80x94has been discarded because it is not feasible, due to the minimum times available to modify the velocity of rotation of the tube and the high inertias in play.
U.S. Pat. No. 5,312,065 shows a coil-forming head comprising a shaped tube of a conventional type associated at outlet with a guide extension consisting of an inner element which rotates with the tube, and of an outer element, which can be fixed or can rotate independently of the tube.
The inner rotary element is spiral shaped and has an open inlet end facing the outlet end of the coil-forming tube.
The function of the inner element is substantially to prolong the guiding action of the coil-forming tube, allowing the efficient formation of a circular trailing-end coil and preventing the formation of loops or hooks.
The inner element is removable, and can be removed in the case of low speed rolling of large diameter product, wherein the function of supplementary guide is not necessary but even harmful.
The outer element consists of a cylindrical screen of a greater diameter than the nominal diameter of the coils; its function is to absorb, through sliding friction, the excess energy possessed by the rolled stock when its trailing end leaves the drawing assembly located upstream of the coil-forming head.
This embodiment is valid in theory, but in practice it has shown itself to be unusable on an industrial scale because it is complex and unreliable, particularly in the case of a high velocity rotary coil-forming head.
Another solution could be to completely eliminate the containing ring, or to make it with a much larger diameter than the terminal diameter of the coil-forming tube, which would allow the trailing-end coil to reach its natural diameter according to the increased velocity acquired.
However, this cannot be achieved for various reasons, including the connected problems of safety for the workers, or the so-called xe2x80x9cchewingxe2x80x9d of the coils caused by the passage of the spiral-shaped terminal end of the coil-forming head over the material which has already been expelled from the tube and is blocked against the ring.
Document DE-A-19 25 800 describes a device to produce reels of rod comprising a guide tube with a vertical axis and equipped with both rotation movement around the vertical axis and also oscillatory movement along the same axis.
Due to the positioning on the vertical axis of the rod guide tube, there are very different problems to be faced compared with coil-forming tubes having a horizontal axis similar to that of the Applicant""s invention, since the problems connected with the increased velocity of the trailing end of the rolled stock are radically different, especially because, in the case of DE""800, the rod enters the tube after having been bent and therefore considerably slowed down.
At outlet from said vertical axis guide tube there is a conical impact hood: as the oscillatory movement of the guide tube along its axis continually varies the reciprocal position of the outlet tube and the conical hood, it allows to continually vary and control the diameter of the coils of the reel being formed.
The device described in DE""800 substantially serves to obtain as compact a reel as possible, preventing interstices from forming and optimising the use of the coiling spaces available.
The impact hood, consisting of segments which can be radially adjusted, is always involved in the process of forming the coils, and not only in the final stage of forming the coils when the trailing end of the rolled stock is subjected to increased velocity.
The present Applicant has devised and embodied this invention to overcome this shortcoming, connected to the increased velocity of the trailing end of a rolled product emerging from a horizontal-axis coil-forming tube, with a simple but extremely efficacious solution.
The invention is set forth and characterised in the main claim while the dependent claims describe other characteristics of the main embodiment.
The purpose of the invention is to achieve a coil-forming head, of the type rotating around a substantially horizontal and longitudinally fixed axis, suitable to improve the conformation of the trailing-end coils, eliminating the problems caused by the increased velocity assumed by the trailing-end segment at the moment when it leaves the drawing devices.
To be more exact, the purpose of the invention is to prevent the formation of the unwanted trailing-end loop, thus obtaining a terminal coil with a substantially circular conformation and therefore eliminating the need for manual straightening and cutting interventions.
A further purpose of the invention is to achieve a simple, economical solution which can be applied substantially to every pre-existing coil-forming head of the type mentioned above, and moreover particularly suitable for small diameter, very high velocity rolled stock.
According to the invention, at the outlet of the shaped tube which forms the coils, rotating around a substantially horizontal axis, there is a substantially coaxial containing ring with a tapering conformation diverging outwards.
The tapering ring is defined by a lesser diameter, facing towards the inside of the coil-forming head, and by a larger diameter, facing towards the outlet of the coil-forming head from which the formed coils are discharged.
The inclination of the taper, according to the invention, is advantageously but not restrictively between 10xc2x0 and 80xc2x0.
The trailing-end coils emerging from the shaped tube, which tend to expand radially due to the increased velocity, are then induced to lie on the inclined plane of the tapering ring and can then gradually vent the kinetic energy acquired.
Therefore, the presence of the tapering ring at the outlet of the coil-forming tube allows to prevent the perpendicular impact of the material against a fixed cylindrical ring, thus preventing the blockage of the material and the consequent formation of the trailing-end loop.
At the same time, the ring ensures in any case containment and protection for the workers, allowing the material to expand gradually and vent its increased velocity, but prevents an excessive, uncontrolled expansion.
Moreover, the material progressively translates towards the outlet of the coil-forming head and hence the last coils formed are not subject to damage deriving from a subsequent passage over the material of the terminal part of the spiral shaped coil-forming head.
In a first embodiment, the containing ring is fixed.
According to a variant, the ring is made to rotate by the mandrel of the coil-forming head.
The trailing-end coils which are obtained with the solution of the invention have a slightly larger diameter than the nominal one, but in any case it is always limited within an acceptable tolerance, and they can thus slow down against the inclined surface of the tapering ring and be discharged onto the discharge belt.
According to one embodiment of the invention, downstream of the diverging tapering ring there is at least a substantially cylindrical segment, the function of which is to stabilize the trailing end coils after they have formed on said tapering ring.